15 The climate of the future

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15The climate of the future
How we forecast the climate of the future Climate
models What models predict about our
future Sources of uncertainty Principles of
Climatology (GEOG31064-Sheridan)
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The future climate

• How do we forecast the climate of the future?
• What are climate models?
• What do they predict about our future?
• What are some of the biggest uncertainties?

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Methods of predicting the future

• Historical changes
• Paleoclimatic analogs
• Global Climate Models (GCMs)

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Methods of predicting the future

• Historical changes 1.0-3.0
• Paleoclimatic analogs 1.4-3.2
• Global Climate Models (GCMs) 2.1-4.8
• Warming (C) with a doubling of CO2

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Goals of weather forecast models

• To predict actual weather conditions over a short
  period of time
• ETA Model
• 12-km grid
• Not global (focused upon US)
• 60 vertical layers
• 6 minutes
• 14 billion calculations for each data point to
  get a 48-hour forecast, for each parameter

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Goals of climate forecast models

• To predict long-term changes in mean fields
  (temperature, pressure, precipitation, storms)
• Do not attempt to predict individual events

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Weather vs. climate models?

• What things to climate models need to account for
  that weather models dont?
• Changes in ocean temperature and heat flux
• Changes in vegetation
• Changes in ice cover
• Long-term changes in atmospheric composition
• Long-term changes in salinity
• Long-term changes in land use

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Climate model issuesFeedbacks

• Ice/albedo
• Clouds
• Water vapor
• Vegetation/albedo

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Climate model issuesTuning out extremes

• Small errors (especially in ocean fluxes) tend to
  build up over time
• GCMs have flux adjustments to keep these ocean
  fluxes and other parameters from getting out of
  hand and biasing the model too far
• What sort of problems might this bring about?

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Climate model issuesClimate equilibrium
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Climate models

• Best handle on atmospheric pressure
• Temperature good, except near poles
• Moisture, cloudiness, precipitation weaker

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So what may happen?
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Types of forecasts

• 2xCO2
• Scenarios Gradual increase in CO2

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Future uncertainties

• A1fi (higher) continued dependence on fossil
  fuels with material-intensive economy
• B1 (lower) shift to alternative energy
  sources with service information-focused
  economy

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Uncertainties climate models
HadCM3 (UK) mid-sensitivity PCM (NCAR) low
sensitivity
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Scenario warming
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Mean temperature changes
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Warmer summers
2020s
2050s
JUNE-JULY-AUGUST TEMPS
2080s
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Chicago heat-wave projections
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Extreme weather
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Seasonal changes
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Moisture parameters
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A wetter and drier world
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Precipitation intensity
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Hurricanes

• Very politically charged debate since Katrina

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Sea ice volume
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Sea-level rise
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Other things

• Middle-latitude storminess
• May increase as upper-level temperature gradient
  increases
• May decrease as surface temperature gradient
  decreases
• Monsoon to increase with land temperature
  increase
• El Nino?
• Tropical cyclones?

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In the long run

• Long-term cooling trend, suggesting the next ice
  age may begin within 10,000 years

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Ranges of impacts
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Model vs. reality
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Issues to consider

• How will climate variability change?
• How do emissions change?
• How does population change?
• Will half of all CO2 still go into the ocean?
• How will the sun vary?